1.

How fast a person should drive his car so that the red signal of light appears green? (Wavelength of red colour = 6200 Å and wavelength for green colour = 5400 Å)

Answer»

`1.5 XX 10^(8)m/s`
`7 xx 10^(7) m/s`
`3.9 xx 10^(7) m/s`
`2 xx 10^(8) m/s`

Solution :Doppler SHIFT (Source moving towwards observer)
`LAMBDA . = lambda(1 - (V)/(C))`
`5400 Å = 6200 Å(1 - (V)/(C))`
`V = [1 - (54)/(62)]C = 3.9 xx 10^(7)` approx.


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